This application is based upon, claims the benefit of priority of, and incorporates by reference the contents of prior Japanese Patent Application No. 2002-72478 filed Mar. 15, 2002.
1. Field of the Invention
The present invention relates to malfunction detection of a water temperature control valve on a water-cooled engine.
2. Description of the Related Art
It is necessary for a water-cooled engine to control its water temperature within an appropriate temperature range in order to run the engine efficiently. Improving the engine""s efficiency is usually accomplished by improving the intake-air filling efficiency and by suppressing increases in friction loss at an operating portion within the engine. To this end, the inventors of the present invention filed a patent application (disclosed as Japanese Unexamined Patent Publication N. 2000-45773) relating to a technique to control engine cooling water temperature within an appropriate temperature range. According to this technique, with the aim of making an actual cooling water temperature follow the target value of the cooling water temperature, a ratio of the flow rate of cooling water from the radiator passage side to the flow rate of cooling water from the bypass passage side is adjusted. The publication discloses a technique to control cooling water temperature to match the target water temperature through this adjustment achieved by feedback controlling an opening degree of a rotary valve.
Recently, vehicle emission control has been enforced in Japan, the European Union, and the United States, and detection of abnormalities in emission-reducing engine components is mandatory. However, as for the technique of using feedback control to control the actual cooling water temperature so that it maintains the target value of the cooling water temperature, a malfunction detecting method for a water temperature control valve has not been established.
It is therefore an object of the present invention to enable malfunction detection of the water temperature control valve used during feedback control of the engine cooling water temperature.
In order to achieve the above and other objects, according to a first aspect of the invention, malfunction of the water temperature control valve is detected based on a cooling water temperature target value and a value of the cooling water temperature while a cooling water temperature control means is controlling the water temperature control valve.
Under such control that makes the cooling water temperature follow the target value, the detected value of the cooling water temperature follows the target value when the water temperature control valve is operating normally. In contrast, in a case where the water temperature control valve is fixed accidentally, for example, the detected value of the cooling water temperature deviates from the target value. It is thus possible to accurately detect a malfunction of the water temperature control valve based on a relationship between the target value and the detected value of the cooling water temperature. Herein, the relation between the target value and the detected value of the cooling water temperature shows that a deviation of the detected value of the cooling water temperature from the target value of the cooling water temperature becomes greater in the event of a malfunction.
According to a second aspect of the invention, a malfunction detecting means is able to accurately detect malfunction of the water temperature control valve based on the deviation of the detected value of the cooling water temperature from the target value of the cooling water temperature.
According to a third aspect of the invention, the malfunction detecting means detects malfunction of the water temperature control valve when the deviation of the value of the cooling water temperature detected by a cooling water temperature detecting means from the target value of the cooling water temperature set by target temperature setting means exceeds a certain threshold value for at least a certain time period.
Because malfunction of the water temperature control valve is judged only when the deviation exceeds the certain judgment threshold value continuously for at least the certain period, it is possible to reduce erroneous judgment due to hunting or the like while the cooling water temperature is controlled.
When the vehicle is running at a high speed or under high-load operating conditions, particular inconveniences may occur. Firstly, when the vehicle is running at a high speed, heat radiation from the radiator passages increase because the air passing through them is increased. Hence, control such that makes the cooling water temperature follow the target value may possibly cause hunting. Secondly, under the high-load operating state, the heat generation amount of the engine increases, and the difference from the target value of the cooling water temperature increases. Hence, hunting may possibly occur when making the cooling water temperature follow the target value of the cooling water temperature. By taking these circumstances into account, in the case of making judgment based on only a deviation of the detected value of the cooling water temperature from the target value of the cooling water temperature, there is a possibility that normal operation of the water temperature control valve may be erroneously judged as abnormal depending on the operating state.
Hence, according to a fourth aspect of the invention, the certain judgment threshold value used to judge a malfunction may preferably be variably set based on the operating state of an internal combustion engine. Consequently, even when response of the water temperature control is changed according to the operating state, erroneous judgment can be reduced by changing the judgment threshold value depending on the operating state.
According to a fifth aspect of the invention, the cooling water temperature detecting means includes a sensor provided to a cooling water passage of the internal combustion engine for outputting the cooling water temperature, and thereby detects the temperature output from the sensor. Also, the cooling water temperature control means adjusts the water temperature control valve in such a manner that the cooling water temperature detected by the cooling water temperature detecting means follows the target value of the cooling water temperature set by the target temperature setting means.
Further, according to a sixth aspect of the invention, the sensor for outputting the cooling water temperature is provided somewhere along a passage from a junction of the radiator passage and a bypass passage to the internal combustion engine.
It is thus possible to accurately control the cooling water temperature which circulates through the internal combustion engine. Hence, not only can filling efficiency of intake air be improved, but also an increase in frictional losses at an operating portion, that is, at the contact portions of moving parts, within the internal combustion engine can be reduced.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.